The use of e-books and other electronic documents are rapidly increasing. E-books, as opposed to traditional books, can be easily updated after they have been sold. For example, a textbook manufacturer can push corrections or other updates to an electronic textbook to users, rather than forcing the users to purchase new versions of the textbook.
With e-books, additional information, such as video or audio content, can be incorporated into the e-book, or can be presented alongside the e-book to the user on whatever device that the user is using to read the e-book. However, identifying such relevant information may be difficult.